RIAA Curve

For the same sound level, a low frequency requires a larger groove which gives two
drawbacks:
- Less recording time
- Difficulties for the cartridge to follow it and thus, higher distorsion

At the other end of the spectrum, the contact between the stylus and the groove makes
noise, a high frequency noise. By increasing the high frequencies level during recording
we can obtain a better signal/noise ratio as the noise is reduced by the playback curve.

The RIAA (Recording Industry Association of America)
introduced the original RIAA equalisation characteristic during the 1960s. Before
this became available several other curves did exist, but since the RIAA curves
introduction they have been replaced

To obtain the original RIAA curve the following equation is used:
Where:
f=frequencyt1=treble time constant, 75uSt2=medium time constant, 318uSt3=bass time constant, 3180uS

In 76', IEC introduced a modification of this curve by introducing a new time constant
that modifies only the extreme bass. It is known as the RIAA/IEC curve.
This correction has never obtained a big success, the original RIAA curve is still the
most widely used.

To obtain the revised RIAA IEC curve the following equation is used:
Where: t4=extreme bass time constant, 7950uS